a rare, radioactive, metallic chemical element, one of the actinides, found in pitchblende: symbol, Pa; at. no. 91
Origin of protactiniumModL: see proto- and actinium
A rare, extremely toxic, radioactive, lustrous, metallic element having more than 30 known isotopes and isomers, the most common of which is Pa-231 with a half-life of 32,760 years. Atomic number 91; atomic weight 231.036; melting point 1,572°C; specific gravity 15.37 (calculated); valence 2, 3, 4, 5. See Periodic Table.
Origin of protactiniumprot(o)- actinium ( so called because it decays into actinium )
- A chemical element (symbol Pa) with atomic number 91.
proto- +"Ž actinium.